Method and device for analysing a structure

ABSTRACT

A method for analyzing a structure, including
         a measurement of a duration T, a mechanical S or acoustic energy S ac  and/or a spatial extension ξ of a sequence and/or a number of mechanical or acoustic events N or N ac  in that sequence and/or of the mechanical A or acoustic A ac  energies of the events of that sequence, and/or   a measurement of a mechanical energy A or acoustic energy A ac  of an event, and/or of a temporal frequency of mechanical events dN/dt or acoustic events dN ac /dt, and/or of a dissipated mechanical energy rate dE/dt or of an acoustic energy rate dE ac /dt at the time of that event, and   according to the measurement of an event and/or the measurement of a sequence of events, a calculation by technical means of a data r representative of a state of health of the structure or of a time t c  to failure of the structure.

TECHNICAL FIELD

The present invention relates to a method for analyzing the mechanical health of a solid or structure. It also relates to a device for carrying out this method.

Such a device allows a user to monitor a structure such as a bridge or a building. The field of the invention is more particularly, but not exclusively, civil engineering, mechanical engineering, and the transport and energy sectors.

PRIOR STATE OF THE ART

Techniques are known according to the state of the art called post-mortem or failure analysis of a structure, which are based on analyzing fragments of a broken material after the failure of that structure.

It is also known that the techniques according to the state of the art are positioned in the field of structure monitoring, which is an engineering science that consists of monitoring the mechanical health of a structure by measuring its mechanical response during its use by means of sensors.

However, as a drawback, such monitoring techniques often lack robustness, being limited to a use case corresponding to a type of material used in a type of structure. Anticipating the failure of structures and solids in contexts as varied as civil engineering with the monitoring of concrete structures or transportation with the monitoring of devices made of metal alloys or polymer-based composites remains a major challenge for engineers.

To implement such an approach, however, there are many sensors that make it possible to “listen to” and monitor the structures over time, such as strain gauges or microphones to record the acoustic signals emitted by the structure. These signals generally show an extremely intermittent change in the mechanical response of structures, characterized by short periods of high activity, separated by periods of silence. This is called “crackling noise”, which shows some similarity with the dynamics of earthquakes. For about twenty years, research has been conducted in an attempt to understand and describe these signals. However, deciphering these signals and thus using them to anticipate the failure of a structure is still out of reach as their statistical properties and their link with the change in the mechanical health of the structure remain poorly understood, which is a drawback.

The purpose of the present invention is to at least partially solve at least one of these drawbacks of the state of the art.

DISCLOSURE OF THE INVENTION

We propose to achieve this goal with a method for analyzing a structure, comprising:

-   -   for at least one sequence of several events located inside the         structure, each event being a mechanical damage event or an         acoustic event:         -   a measurement of a sequence of said events comprising a             measurement by technical means of measurement of a duration             T, a mechanical S or acoustic energy S_(ac) and/or a spatial             extension ξ of that sequence and/or a number of mechanical N             or acoustic N_(ac) events in that sequence and/or of the             mechanical A or acoustic A_(ac) energies of the events of             that sequence, and/or         -   a measurement of an event comprising a measurement by the             technical means of measurement of a mechanical energy A or             acoustic energy A_(ac) of this event, and/or of a temporal             frequency of mechanical events dN/dt or acoustic events             dN_(ac)/dt at the time of this event, and/or of a dissipated             mechanical energy rate dE/dt or of an acoustic energy rate             dE_(ac)/dt at the time of this event and     -   according to the measurement of an event and/or the measurement         of a sequence of events, a calculation by technical means of         calculation of a data r representative of a state of health of         the structure or of a time t_(c) to failure of the structure.

The measurement of a sequence of events may comprise a measurement by the technical means of measurement of a duration T of that sequence of events.

The measurement of a sequence of events may comprise a measurement by the technical means of measurement of a mechanical energy S or acoustic energy S_(ac) of that sequence of events.

The measurement of mechanical energy S or acoustic energy S_(ac) can be obtained by several sensors spatially distributed around and/or inside the structure.

The measurement of a sequence of events may comprise a measurement by the technical means of measurement of a spatial extension ξ of that sequence of events.

The measurement of an event may comprise a measurement by the technical means of measurement of a mechanical energy A or acoustic energy A_(ac) of that event.

The measurement of a sequence of events may comprise a measurement by the technical means of measurement of the number of mechanical events N or acoustic events N_(ac) in that sequence.

The measurement of an event may comprise a measurement by the technical means of measurement of a time frequency of mechanical events dN/dt or acoustic events dN_(ac)/dt.

The measurement of an event may include a measurement by the technical means of a dissipated mechanical energy rate dE/dt or an acoustic energy rate dE_(ac)/dt.

The calculation may comprise a calculation of the data r representative of the health status of the structure.

The data r can be calculated as equal to or proportional to the ratio ξ/L where L is a characteristic size of the structure or material composing the structure and ξ the measurement of a spatial extension ξ of a sequence of events.

The data r can be calculated as equal to or proportional to the ratio ξ/L where L is a characteristic size of the structure or material composing the structure, ξ depending on the measurement of the energy respectively S or S_(ac) of a sequence of events, ξ depending on:

-   -   a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or     -   respectively S or S_(ac) by a relation relating ξ to S^(1/df) or         S_(ac) ^(1/(α·df)) respectively,         d_(f) being a constant, α being a constant         ξ depending on S or S_(ac) preferably respectively by the         relation:         respectively d₀·(S/A₀)^(1/df)=ξ or

d ₀·(S _(ac) /A _(ac0))^(1/(α·df))=ξ

a may be substantially equal to 2.6, and/or d_(f) may be substantially equal to 1.1 for a two-dimensional structure and substantially equal to 1.5 for a three-dimensional structure.

The data r can be calculated as equal to or proportional to the ratio ξ/L where L is a characteristic size of the structure or material composing the structure, ξ depending on the measurement of the duration T of a sequence of events, ξ depending on:

-   -   a constant τ₀ and a constant d₀, and/or     -   T by a relation relating ξ to (T)^(1/z), z being a constant         preferably substantially equal to 0.57,         ξ preferably depending on T by the relation ξ=(T/τ₀)^(1/z)·d₀

In particular, the system according to the invention may comprise:

-   -   a measurement of τ₀ as the smallest measured event duration of         the at least one sequence, and/or     -   a measurement of A₀ or A_(ac0) respectively as the energy of the         smallest mechanical or acoustic events measured from the at         least one sequence.

The data r can be calculated as equal to or proportional to the ratio ξ/L where L is a characteristic size of the structure or material of the structure, ξ depending on the measurement of the respectively mechanical A or acoustic A_(ac) energy of that event, ξ depending on:

-   -   a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or     -   respectively A or A_(ac) by a relation relating ξ to A^(2/df) or         A_(ac) ^(2/(α·df)) respectively,         d_(f) being a constant, α being a constant         ξ depending on A or A_(ac) respectively preferably by the         relation:         respectively d₀·(A/A₀)^(2/df)=ξ or

d ₀·(A _(ac) /A _(ac0))^(2/(α·df))=ξ

The data r can be calculated as equal to or proportional to the ratio ξ/L where L is a characteristic size of the structure or material of the structure, ξ depending on the measurement of the number of respectively mechanical N or acoustic N_(ac) events in that sequence, ξ depending on:

-   -   a constant d₀, and/or     -   respectively N or N_(ac) by a relation relating ξ to N^(2/df) or         N_(ac) ^(2/(α·df)) respectively,         d_(f) being a constant, α being a constant         ξ depending on N or N_(ac) respectively preferably by the         relation:         respectively d₀·(N)^(2/df)=ξ or

d ₀·(N _(ac))^(2/(α·df))=ξ

The data r can be calculated as equal or proportional to the ratio ξ/L with L a characteristic size of the structure or material composing the structure, ξ depending on the measurement of the frequency of respectively mechanical dN/dt or acoustic dN_(ac)/dt events, ξ depending on:

-   -   a constant ΔT₀ and a constant d₀, and/or     -   respectively dN/dt or dN_(ac)/dt by a relation relating ξ to         (dN/dt)^(2/df) or (dN_(ac)/dt)^(2/(α·df)) respectively, d_(f)         being a constant, α being a constant         ξ depending on dN/dt or dN_(ac)/dt respectively preferably by         the relation:         respectively d₀·(ΔT₀·dN/dt)^(2/df)=ξ or

d ₀·(ΔT ₀ ·dN _(ac) /dt)^(2/(α·df))=ξ

The data r can be calculated as equal or proportional to the ratio ξ/L with L a characteristic size of the structure or material composing the structure, ξ depending on the measurement of a dissipated mechanical energy rate dE/dt or an acoustic energy rate dE_(ac)/dt, ξ depending on:

-   -   a constant respectively ΔT_(a0) or ΔT_(ac0), and a constant d₀,         and/or     -   respectively dE/dt or dE_(ac)/dt by a relation relating ξ to         (dE/dt)^(1/df) or (dE_(ac)/dt)^(1/(α·df)), d_(f) respectively, α         being a constant         ξ depending on dE/dt or dE_(ac)/dt respectively preferably by         the relation:         respectively d₀·(ΔT_(a0)·dE/dt)^(1/df)=ξ or

d ₀·(ΔT _(ac0) ·dE _(ac) /dt)^(1/(α·df))=ξ

The calculation can include the calculation of the time t_(c).

The measurement of a sequence of events or the measurement of an event can be measured at a measurement time t, the calculation of the time t_(c) preferably comprising a use and/or an interpolation and/or a regression of a function (the expression interpolation and/or a regression of a function can mean here generally a description by a function) connecting t_(c), t and one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt (and even optionally dE/dt and dE_(ac)/dt) or the temporal evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt (and even optionally dE/dt and dE_(ac)/dt)

-   -   said function preferably comprising:     -   S=B₀/(t_(c)−t)^(β) where B₀ is a constant, or     -   A=C₀/(t_(c)−t)^(β/2) where C₀ is a constant, or     -   T=D₀/(t_(c)−t)^(β·z/df) where D₀ is a constant, or     -   ξ=E₀/(t_(c)−t)^(β/df) where E₀ is a constant, or     -   N=F₀/(t_(c)−t)^(β/2) where F₀ is a constant, or     -   dN/dt=G₀/(t_(c)−t)^(β/2) where G₀ is a constant, or     -   S_(ac)=H₀/(t_(c)−t)^(αβ) where H₀ is a constant, or     -   A_(ac)=K₀/(t_(c)−t)^(αβ/2) where K₀ is a constant, or     -   N_(ac)=L₀/(t_(c)−t)^(αβ/2) where L₀ is a constant, or     -   dN_(ac)/dt=M₀/(t_(c)−t)^(αβ/2) where M₀ is a constant, or     -   dE/dt=N₀/(t_(c)−t)^(β) where N₀ is a constant, or     -   dE_(ac)/dt=O₀/(t_(c)−t)^(αβ) where O₀ is a constant,     -   where preferably β=0.5 and α=2.6.

The measurement of event sequences or the measurement of events may be measured in such a way as to determine and/or track a time evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt (and even optionally dE/dt and dE_(ac)/dt) as a function of the measurement time t, the calculation of the time t_(c) preferably comprising a use and/or an interpolation and/or a regression of a function (the expression interpolation and/or regression of a function can mean here generally a description by a function) relating t_(c), t and the temporal evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt (and even optionally dE/dt and dE_(ac)/dt)

-   -   said function preferably comprising:     -   S=B₀/(t_(c)−t)^(β) where B₀ is a constant, or     -   A=C₀/(t_(c)−t)^(β/2) where C₀ is a constant, or     -   T=D₀/(t_(c)−t)^(β·z/df) where D₀ is a constant, or     -   ξ=E₀/(t_(c)−t)^(β/df) where E₀ is a constant, or     -   N=F₀/(t_(c)−t)^(β/2) where F₀ is a constant, or     -   dN/dt=G₀/(t_(c)−t)^(β/2) where G₀ is a constant, or     -   S_(ac)=H₀/(t_(c)−t)^(αβ) where H₀ is a constant, or     -   A_(ac)=K₀/(t_(c)−t)^(αβ/2) where K₀ is a constant, or     -   N_(ac)=L₀/(t_(c)−t)^(αβ/2) where L₀ is a constant, or     -   dN_(ac)/dt=M₀/(t_(c)−t)^(αβ/2) where M₀ is a constant, or     -   dE/dt=N₀/(t_(c)−t)^(β) where N₀ is a constant, or     -   dE_(ac)/dt=O₀/(t_(c)−t)^(αβ) where O₀ is a constant,     -   where preferably β=0.5 and α=2.6.

Preferably, there is a ratio greater than or equal to two between the smallest and largest values of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt, dN_(ac)/dt, dE/dt or dE_(ac)/dt recorded.

Each sequence of events preferably comprises at least three events.

According to still another aspect of the invention, proposed is a structure analysis device comprising:

-   -   for at least one sequence of several events located inside the         structure, each event being a mechanical damage event or an         acoustic event, technical means of measurement:         -   arranged to measure a sequence of said events comprising a             measurement by technical means of a duration T, a mechanical             S or acoustic energy S_(ac) and/or a spatial extension ξ of             that sequence and/or a number of mechanical N or acoustic             N_(ac) events in that sequence and/or of the mechanical A or             acoustic A_(ac) energies of the events of that sequence,             and/or         -   arranged to measure an event comprising a measurement by the             technical means of measurement of a mechanical energy A or             acoustic energy A_(ac) of this event, and/or of a temporal             frequency of mechanical events dN/dt or acoustic events             dN_(ac)/dt at the time of this event, and/or of a dissipated             mechanical energy rate dE/dt or of an acoustic energy rate             dE_(ac)/dt at the time of this event and     -   computing means arranged and/or programmed to compute, as a         function of the measurement of an event and/or the measurement         of a sequence of events, a data r representative of a state of         health of the structure or of a time t_(c) to failure of the         structure.

The technical means of measurement can be arranged to carry out a measurement of a duration T of this sequence of events.

The technical means of measurement can be arranged to carry out a measurement of a mechanical energy S or acoustic energy S_(ac) of that sequence of events.

The technical means of measurement may comprise several sensors spatially distributed around and/or inside the structure.

The technical means of measurement can be arranged to carry out a measurement of a spatial extension ξ of this sequence of events.

The technical means of measurement can be arranged to perform a measurement of a mechanical energy A or acoustic energy A_(ac) of this event.

The technical means of measurement can be arranged to perform a measurement of the number of mechanical events N or acoustic events N_(ac) in that sequence.

The technical means of measurement can be arranged to perform a measurement of a time frequency of mechanical events dN/dt or acoustic events dN_(ac)/dt.

The technical means of measurement can be arranged to perform a measurement of a dissipated mechanical energy rate dE/dt or an acoustic energy rate dE_(ac)/dt.

The computing means can be arranged and/or programmed to compute the data r representative of the health status of the structure.

The computing means may be arranged and/or programmed to compute the data r as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or material composing the structure and ξ the measure of a spatial extension ξ of a sequence of events.

The computing means may be arranged and/or programmed to compute the data r as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or material composing the structure, ξ depending on the measurement of the energy respectively S or S_(ac) of a sequence of events, ξ depending on:

-   -   a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or     -   respectively S or S_(ac) by a relation relating ξ to S^(1/df) or         S_(ac) ^(1/(α·d) _(f)) respectively,         d_(f) being a constant, α being a constant         ξ depending on S or S_(ac) respectively preferably by the         relation:         respectively d₀·(S/A₀)^(1/df)=ξ or

d ₀·(S _(ac) /A _(ac0))^(1/(α·df))=ξ

α is preferably substantially equal to 2.6, and/or d_(f) is preferably substantially equal to 1.1 for a two-dimensional structure and substantially equal to 1.5 for a three-dimensional structure.

The computing means may be arranged and/or programmed to compute the data r as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or material composing the structure, ξ depending on the measurement of the duration T of a sequence of events, ξ depending on:

-   -   a constant τ₀ and a constant d₀, and/or     -   T by a relation relating ξ to (T)^(1/z), z being a constant         preferably substantially equal to 0.57,         ξ preferably depending on T by the relation ξ=(T/τ₀)^(1/z)·d₀

The technical means of measurement can be arranged to perform:

-   -   a measurement of τ₀ as the smallest measured event duration of         the at least one sequence, and/or     -   a measurement of A₀ or A_(ac0) respectively as the energy of the         smallest mechanical or acoustic events measured from the at         least one sequence.

The computing means may be arranged and/or programmed to compute the data r as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or material of the structure, ξ depending on the measurement of the energy respectively A or A_(ac) of that event, ξ depending on:

-   -   a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or     -   respectively A or A_(ac) by a relation relating ξ to A^(2/df) or         A_(ac) ^(2/(α·df)) respectively,         d_(f) being a constant, α being a constant         ξ depending on A or A_(ac) respectively preferably by the         relation:         respectively d₀·(A/A₀)^(2/df)=ξ or

d ₀·(A _(ac) /A _(ac0))^(2/(α·df))=ξ

The computing means may be arranged and/or programmed to compute the data r as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or material of the structure, ξ depending on the measurement of the energy respectively N or N_(ac) of that event, ξ depending on:

-   -   a constant d₀, and/or     -   respectively N or N_(ac) by a relation relating ξ to N^(2/df) or         N_(ac) ^(2/(α·df)) respectively,         d_(f) being a constant, α being a constant         ε depending on N or N_(ac) respectively preferably by the         relation:         respectively d₀·(N)^(2/df)=ξ or

d ₀·(N _(ac))^(2/(α·df))=ξ

The computing means may be arranged and/or programmed to compute the data r as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or material of the structure, ξ depending on the measurement of the frequency of respectively mechanical dN/dt or acoustic dN_(ac)/dt events, ξ depending on:

-   -   a constant ΔT₀ and a constant d₀, and/or     -   respectively dN/dt or dN_(ac)/dt by a relation relating ξ to         (dN/dt)^(2/df) or (dN_(ac)/dt)^(2/(α·df)) respectively, d_(f)         being a constant, α being a constant         ξ depending on dN/dt or dN_(ac)/dt respectively preferably by         the relation:         respectively d₀·(ΔT₀·dN/dt)^(2/df)=ξ or

d ₀·(ΔT ₀ ·dN _(ac) /dt)^(2/(α·df))=ξ

The computing means can be arranged and/or programmed to compute the data r as equal or proportional to the ratio ξ/L with L a characteristic size of the structure or material composing the structure, ξ depending on the measurement of a dissipated mechanical energy rate dE/dt or an acoustic energy rate dE_(ac)/dt, ξ depending on:

-   -   a constant respectively ΔT_(a0) or ΔT_(ac0), and a constant d₀,         and/or     -   respectively dE/dt or dE_(ac)/dt by a relation relating ξ to         (dE/dt)^(1/df) or (dE_(ac)/dt)^(1/(α·d) _(f)), d_(f)         respectively, α being a constant         ξ depending on dE/dt or dE_(ac)/dt respectively preferably by         the relation:         respectively d₀·(ΔT_(a0)·dE/dt)^(1/df)=ξ or

d ₀·(ΔT _(ac0) ·dE _(ac) /dt)^(1/(α·df))=ξ

The computing means can be arranged and/or programmed to compute the time t_(c).

The technical means of measurement can be arranged to carry out the measurement of a sequence of events or the measurement of an event at a measurement time t, the computing means preferably being arranged and/or programmed to compute the time t_(c) by a use and/or an interpolation and/or a regression of a function (the expression interpolation and/or regression of a function can mean here generally a description by a function) relating t_(c), t and one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt et dN_(ac)/dt (and even optionally dE/dt and dE_(ac)/dt) or the temporal evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac) dN/dt and dN_(ac)/dt (and even possibly dE/dt and dE_(ac)/dt)

-   -   said function preferably comprising:     -   S=B₀/(t_(c)−t)^(β) where B₀ is a constant, or     -   A=C₀/(t_(c)−t)^(β/2) where C₀ is a constant, or     -   T=D₀/(t_(c)−t)^(β·z/df) where D₀ is a constant, or     -   ξ=E₀/(t_(c)−t)^(β/df) where E₀ is a constant, or     -   N=F₀/(t_(c)−t)^(β/2) where F₀ is a constant, or     -   dN/dt=G₀/(t_(c)−t)^(β/2) where G₀ is a constant, or     -   S_(ac)=H₀/(t_(c)−t)^(α·β) where H₀ is a constant, or     -   A_(ac)=K₀/(t_(c)−t)^(α·β/2) where K₀ is a constant, or     -   N_(ac)=L₀/(t_(c)−t)^(α·β/2) where L₀ is a constant, or     -   dN_(ac)/dt=M₀/(t_(c)−t)^(α·β/2) where M₀ is a constant, or     -   dE/dt=N₀/(t_(c)−t)^(β) where N₀ is a constant, or     -   dE_(ac)/dt=O₀/(t_(c)−t)^(α·β) where O₀ is a constant,     -   where preferably β=0.5 and α=2.6.

The technical means of measurement may be arranged to measure the sequence of events or the measurement of events is measured in such a way as to determine and/or track a time evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt (and even optionally dE/dt and dE_(ac)/dt) as a function of the measurement time t, the technical means of measurement preferably being arranged and/or programmed to compute the time t_(c) preferably comprising a use and/or an interpolation and/or a regression of a function (the expression interpolation and/or regression of a function can mean here generally a description by a function) relating t_(c), t and the temporal evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt (and even optionally dE/dt and dE_(ac)/dt)

-   -   said function preferably comprising:     -   S=B₀/(t_(c)−t)^(β) where B₀ is a constant, or     -   A=C₀/(t_(c)−t)^(β/2) where C₀ is a constant, or     -   T=D₀/(t_(c)−t)^(β·z/df) where D₀ is a constant, or     -   ξ=E₀/(t_(c)−t)^(β/df) where E₀ is a constant, or     -   N=F₀/(t_(c)−t)^(β/2) where F₀ is a constant, or     -   dN/dt=G₀/(t_(c)−t)^(β/2) where G₀ is a constant, or     -   S_(ac)=H₀/(t_(c)−t)^(α·β) where H₀ is a constant, or     -   A_(ac)=K₀/(t_(c)−t)^(α·β/2) where K₀ is a constant, or     -   N_(ac)=L₀/(t_(c)−t)^(α·β/2) where L₀ is a constant, or     -   dN_(ac)/dt=M₀/(t_(c)−t)^(α·β/2) where M₀ is a constant, or     -   dE/dt=N₀/(t_(c)−t)^(β) where N₀ is a constant, or     -   dE_(ac)/dt=O₀/(t_(c)−t)^(α·β) where O₀ is a constant,     -   where preferably β=0.5 and α=2.6.

Preferably, there is a ratio greater than or equal to two between the smallest and largest values of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt, dN_(ac)/dt, dE/dt or dE_(ac)/dt recorded.

Each sequence of events preferably comprises at least three events.

DESCRIPTION OF FIGURES AND EMBODIMENTS

Other benefits and features shall become evident upon examining the detailed description of entirely non-limiting embodiments and implementations, and from the following enclosed drawings:

FIG. 1 shows on its part (a) a first embodiment of a device according to the invention analyzing a structure 5, and is the preferred embodiment of a device according to the invention, and on its part (b) a close-up of the structure

FIG. 2 shows the mechanical response of the structure of FIG. 1 as well as, on part (a) the acoustic signal recorded during the loading of the structure highlighting the sequences of acoustic events of energy S_(ac), and on part (b) the evolution of the dissipated mechanical energy highlighting the sequences of mechanical damage events of energy S.

FIG. 3 shows the method used to measure the energy S of the mechanical event sequences from the mechanical response in FIG. 2 ,

FIG. 4 is a close-up of one of the acoustic event sequences of the acoustic signal in FIG. 2(a),

FIG. 5 is a close-up of an acoustic event during the sequence in FIG. 4 , this event being marked by a star 12 in FIG. 4 ,

FIG. 6 shows the shape of each of the cells composing the structure of FIG. 1 as it is loaded in FIG. 2 , this shape being followed during the loading with a camera, so that their level of damage can be tracked,

FIG. 7 shows the method used to measure the spatial extension of three sequences of different sizes that took place at different times from the images provided by the camera,

FIG. 8 shows the evolution of (a) the energy of the mechanical damage event sequences, (b) their spatial extension, (c) the energy of the acoustic event sequences, (d) the energy of the acoustic events, and (e) the number of acoustic events per sequence measured during a typical experiment, with the rupture taking place around 540 s, when ξ reaches the size L of the structure,

FIG. 9 shows the determination of the spatial extension ξ of the sequences from (a) the mechanical energy S of the mechanical sequences, (b) their acoustic energy S_(ac), (c) the energy A_(ac) of the acoustic events, and (d) the number of acoustic events N_(ac) per sequence measured during an experiment and plotted on the different panels of FIG. 8 ; the breakup occurs around 540 s, when both ξ_(S), ξ_(Sac), ξ_(Aac) and ξ_(Nac) reach the size L of the structure,

FIG. 10 shows in its part (a) a prediction of the time to failure to from the evolution of the mechanical energy S of the sequences over the time range t<t_(cur) and on its part (b) the predicted time t_(c) ^(predicted) as a function of t_(cur) and compared with the time to failure t_(c) actually measured during the experiment,

FIG. 11 shows, as a function of the residual lifetime (t_(c)−t) of the structure, the evolution of (a) the mechanical energy S of the sequences, (b) their acoustic energy S_(ac), (c) the energy A of the damage events, (d) the energy A_(ac) of the acoustic events, (e) the temporal frequency of the damage events dN/dt, (f) the temporal frequency of the acoustic events dN_(ac)/dt, and (g) the spatial extension ξ of the sequences. The power laws represented by straight lines in this logarithmic representation can be used to predict the time to break to by following the procedure described with reference to FIG. 10 ,

FIG. 12 shows different data making it possible to distinguish two successive elementary events belonging to two different sequences, and

FIG. 13 is an experimental proof of concept of the suitability of the method according to the invention for more complex materials (such as gypsum) than the 2D cellular material of FIG. 1 or 6 .

These embodiments are in no way limiting, and in particular, it is possible to consider variants of the invention that comprise only a selection of the features disclosed hereinafter in isolation from the other features disclosed (even if that selection is isolated within a phrase comprising other features), if this selection of features is sufficient to confer a technical benefit or to differentiate the invention with respect to the prior state of the art. This selection comprises at least one preferably functional feature which lacks structural details, and/or only has a portion of the structural details if that portion is only sufficient to confer a technical benefit or to differentiate the invention with respect to the prior state of the art.

First, with reference to FIGS. 1 to 13 , a first embodiment of a device 1 according to the invention implementing a first embodiment of a method according to the invention will be described.

The device 1 is based on the quantitative understanding of the link between the intermittency observed during the mechanical response of solids and structures and the evolution of the mechanical health of such a solid or structure. In particular, it takes advantage of this precise understanding to prevent the failure of structures based on the statistical processing of mechanical and acoustic signals.

The present invention enables the mechanical response of a material or structure 5 to be deciphered in order to predict its failure before it occurs. Solids and structures subjected to external compression or shear exhibit the following mode of failure: they become progressively damaged up to a certain localization threshold (corresponding to a critical load level) beyond which this damage localizes according to a localization band. Beyond this threshold, the material or structure is no longer able to withstand mechanical stresses: the deformations accumulate along a band that runs from one end of the sample to the other, and the material separates into two distinct parts: this is called structural failure or break. If not anticipated, this failure can have dramatic consequences, both from an economic and a safety point of view.

In the case of a traction exerted on the structure 5, the failure will be caused by the initiation, then the propagation of a crack. The present invention enables the prediction of crack initiation from the statistical processing of signals emitted by the structure.

The device 1 for analyzing a structure 5, comprises:

-   -   for at least one sequence 10 of several events located inside         the structure 5, each event being a mechanical damage event or         an acoustic event 11, technical means 2 of measurement:         -   arranged to measure a sequence of said events comprising a             measurement by technical means of a duration T, a mechanical             S or acoustic energy S_(ac) and/or a spatial extension ξ of             that sequence and/or a number of mechanical N or acoustic             N_(ac) events in that sequence and/or of the mechanical A or             acoustic A_(ac) energies of the events of that sequence,             and/or         -   arranged to measure an event comprising a measurement by the             technical means of measurement of a mechanical energy A or             acoustic energy A_(ac) of this event, and/or of a temporal             frequency of mechanical events dN/dt or acoustic events             dN_(ac)/dt at the time of this event, and/or of a dissipated             mechanical energy rate dE/dt or of an acoustic energy rate             dE_(ac)/dt at the time of this event and     -   computing means 3 arranged and/or programmed to compute, as a         function of the measurement of an event and/or the measurement         of a sequence of events, a data r representative of a state of         health of the structure or of a time t_(c) to failure of the         structure.

Each of the means of the device 1 is a technical means.

Typically, the computing means 3 comprise at least one computer, a central processing or computing unit, an analog electronic circuit (preferably dedicated), a digital electronic circuit (preferably dedicated), and/or a microprocessor (preferably dedicated), and/or software means.

The time to can be an instant (for example date and/or time) when the failure or break of the structure is predicted to occur, or a temporal distance (duration, for example in 3 months, 7 days and 15 hours) to the failure or break of the structure.

We consider the quantity L to which is compared in order to evaluate the mechanical health of the structure:

-   -   if the structure 5 is under compression: L is the characteristic         size of the structure according to the direction wherein the         localization band will emerge. In the example shown in FIG. 1 ,         the localization band is oriented along the horizontal axis,         perpendicular to the direction of application of the external         force F_(ext), which is applied along the vertical axis. The         length L is therefore the size of the structure along the         horizontal axis, that is its width, as shown in FIG. 1 b.     -   if the structure 5 is under compression: L is a characteristic         size of the material composing the structure, given by the         relation L=pi/8 (K_(c)/σ_(c))² where K_(c) is the toughness of         the material (in Pa·m^(1/2)) and α_(c) is the tensile stress at         break of the material (or cohesive stress) (in Pa). L is also         called the length of the cohesive zone, and represents the size         of the damaged zone present in front of a crack. In practice,         this size varies from a few hundred microns for metal alloys to         a few millimeters for concrete.

We will consider hereafter the case of L for a force in compression, but the present description remains valid for an L as defined above for a force F_(ext) in traction, the structure being able to be monitored by the method according to the invention in compression or traction (or both at the same time, the method according to the invention being then implemented simultaneously twice respectively for the two different definitions of L of the structure 5 in compression or in structure)

FIG. 1 is a photo of a parallelepipedic structure 5 of size L=18 cm under compression. It is made of a cellular material composed of about 1300 elastic hollow polymer cylinders and is subjected to a uni-axial compressive loading 4.

Each of the references 22 of the measuring means 2 in FIG. 1 is an acoustic sensor arranged to measure the acoustic energy A_(ac) of the acoustic events occurring during the damage of the structure 5 preceding its failure.

In this variant, the means 2 may comprise:

-   -   at least one acoustic sensor 22, which makes it possible to         measure the acoustic energy S_(ac) of the sequences, their         duration T, the acoustic energy A_(ac) of the events         constituting the sequences, their temporal frequency dN_(ac)/dt         as well as the number N_(ac) of acoustic events per sequence,         and/or     -   video and/or ultrasound and/or echographic and/or X-ray or other         imaging means 6 in order to visualize the structure in two or         three dimensions, the imaging means 6 make it possible to         measure the spatial extension ξ of the sequences, their         mechanical energy S, their duration T, the mechanical energy A         of the damage events constituting the sequences, their temporal         frequency dN/dt as well as their number N per sequence, and/or     -   sensors or gauges of deformation or force which allow to measure         the mechanical energy S of the sequences, their duration T, the         mechanical energy A of the damage events constituting the         sequences, their temporal frequency dN/dt, as well as their         number N per sequence.         ξ (also called “dynamic length”) cannot be measured from a         single image. On the contrary, its measurement requires a         succession of images, because it is obtained from the spatial         distribution of a set of successive elementary events belonging         to the same sequence. In this sense, it is different from a         characteristic size that could be extracted from a single image         (such as the image of the cumulative damage field at a given         time). For this reason, it is said to characterize the size of         the dynamic heterogeneities of the damage field, dynamic         heterogeneities that can only be revealed by monitoring the         evolution of the damage field in the structure over a certain         period of time.

The device 1, in particular the measuring means 2 and/or the computing means 3, are arranged and/or programmed to implement the steps of the first method embodiment according to the invention described below.

The invention has been developed from a theoretical and experimental point of view. For the experiments, a 2D model material, a stack of elastic hollow cylinders, was considered, which gives rise to the localization of damage under a sufficiently high stress level, but the present description can be extended to the 3D case.

This system allows a precise characterization of the progress of the damage thanks to:

-   -   (i) a camera 6 that films the progress of the deformation and         damage of the cylinders during the loading     -   (ii) the precise measurement of the force 4 and the displacement         imposed on the sample 5, which makes it possible to deduce the         energy dissipated by damage in the material during the loading.         It was thus shown that the progress of the energy dissipated by         damage during loading was very intermittent, although the         loading itself was increased slowly and regularly. Thus,         localized damage “events” in both space and time take place in         material 5, and are separated by periods of silence, where the         loading of the material is purely elastic. The statistical         properties of these damage events are remarkable: far from the         failure threshold, they are relatively small. But as the         breaking point approaches, their energy becomes greater and         greater. Thus, by representing the energy A of these events as a         function of the distance to localization, it was thus possible         to highlight laws allowing the determination of a data r         representative of a state of health of the structure or a time         t_(c) to failure of the structure.

In the present description, “event” or “elementary event” means a mechanical event or an acoustic event.

A “mechanical event” or “damage event” is defined as a localized inelastic deformation within the structure, this event being localized both in space (within the structure) and in time, and being characterized by:

-   -   its energy A     -   its duration τ₀

An “acoustic event” is defined as a localized vibration or sound signal generated within the structure 5, this event being localized both in space (within the structure) and in time, and being characterized by:

-   -   its energy A_(ac)     -   its duration τ_(ac0)

In the present description, a “sequence” is defined as a group of several events taking place successively in time.

The sequences of acoustic events are made up of a succession of elementary acoustic events which are the consequence of each other. These sequences are characterized by:

-   -   their energy S_(ac) (in aJ)     -   their duration T (in ms)     -   their spatial extension ξ (in mm)     -   the number N_(ac) of acoustic events composing the sequence

The elementary acoustic events that make up the sequences are characterized by:

-   -   their energy A_(ac) (in aJ)     -   their duration τ_(ac0) (in ms)

The sequences of damage events are made up of a succession of elementary damage events which are the consequence of each other. These sequences are characterized by:

-   -   their energy S (in mJ)     -   their duration T (in ms)     -   their spatial extension ξ (in mm)     -   the number N of damage events composing the sequence

These four quantities increase as the structure 5 temporally approaches the break.

A sequence can be defined both mechanically and acoustically in the following way:

-   -   as shown in FIG. 12 , two successive elementary events are         defined as belonging to two different sequences if the waiting         time between them is greater than τ*_(w)/4 where the critical         waiting time τ*_(w) is defined in FIG. 12 as the waiting time         corresponding to the change of regime on the waiting time         distribution. Thus:     -   the waiting times between two successive elementary events are         measured, which provides a set of waiting time values {τ_(w)}         (obtained in general at the beginning of the structure's life,         i.e. quite far from its time to break).     -   the probability density (that is the histogram) P(τ_(w)) of         these waiting times is plotted on a logarithmic scale (see FIG.         12(c))     -   two regimes are observed: for short waiting times, the         distribution is described by a power law P(τ_(w))˜1/(τ_(w))^(κ1)         with an exponent κ1 close to 0.8 (left-hand graph in FIG.         12(c)). For long waiting times, the distribution follows a power         law P(τ_(w))˜1/(τ_(w))^(κ2) with an exponent κ2 close to 2. The         point of intersection between the two power law regressions         provides the characteristic waiting time τ*_(w) which is then         divided by 4 to find the critical waiting time between two         events belonging to two distinct sequences. This definition is         shown in FIG. 12(a) where we see sequences (with different         colors) comprising elementary events whose waiting times         (between each of them) are well below τ*_(w)     -   FIG. 12(b) represents the distribution of waiting times between         elementary events belonging to the same sequence (left graph)         and the distribution of waiting times between sequences (right         graph). FIG. 12(c) is the distribution obtained once all the         waiting times are combined (the one available before it is         possible to separate the sequences from each other).

There are tests that can be used to verify that the sequences have been correctly identified:

-   -   the distribution of waiting times between sequences of the same         mechanical or acoustic type (time separating two successive         sequences) must follow an exponential law. It will be power-law         distributed if the sequences have not been correctly identified.     -   The frequency of the sequences, that is their number per time         interval, is constant and does not vary with the distance to the         break. It will be increased by power law if the sequences have         not been correctly identified.

The dissipated mechanical energy rate dE/dt is calculated as follows: the total dissipated energy is calculated as the sum ΔE of the energy A of the elementary events over a time interval Δt, whose size is chosen as the minimum of the two values among:

-   -   10 times the typical waiting time τ*_(w) or     -   the smallest time interval during which at least 10 events have         been recorded.

The rate of dissipated mechanical energy is then equal to the ratio ΔE/Δt (similarly for dE_(ac)/dt). These two quantities also increase as the failure of the structure 5 gets closer in time.

We will use the following nomenclature in the description:

TABLE 1 L: Characteristic length L as defined above depending on whether structure is under compression or traction t: Time at which the measurement is made t_(c): Time to failure of the structure ξ: Sequence extension S: Energy of a sequence T: Duration of a sequence ΔT₀: Average time between two sequences ξ_(x): Spatial extension of a sequence inferred from the measurement x characterizing that sequence (energy, duration, etc.) d₀: Spatial extension of the smallest damage events A: Energy of a damage event dN/dt: Frequency of damage events N: Number of damage events included in a sequence A₀: Energy of the smallest damage events τ₀: Characteristic duration of a damage event τ_(aco:) Characteristic duration of an acoustic event S_(ac): Acoustic energy of a sequence A_(ac): Acoustic energy of an elementary acoustic event N_(ac): Number of elementary acoustic events included in a sequence dN_(ac)/dt: Frequency of elementary acoustic events

Thus, the first embodiment of a method for analyzing a structure 5 according to the invention, comprises:

-   -   for at least one sequence 10 of several events located inside         the structure 5, each event being a mechanical damage event 11         or an acoustic event:         -   a measurement of a sequence of said events comprising a             measurement by technical means 2 of a duration T, a             mechanical S or acoustic energy S_(ac) and/or a spatial             extension ξ of that sequence and/or a number of mechanical N             or acoustic or N_(ac) events in that sequence and/or of the             mechanical A or acoustic A_(ac) energies of the events of             that sequence, and/or         -   a measurement of an event comprising a measurement by the             technical means of measurement of a mechanical energy A or             acoustic energy A_(ac) of this event, and/or of a temporal             frequency of mechanical events dN/dt or acoustic events             dN_(ac)/dt at the time of this event, and/or of a dissipated             mechanical energy rate dE/dt or of an acoustic energy rate             dE_(ac)/dt at the time of this event and     -   according to the measurement of an event and/or the measurement         of a sequence of events, a calculation by technical means 3 of a         data r representative of a state of health of the structure or         of a time t_(c) to failure of the structure.

The measurement of a sequence of events comprises:

-   -   in a first variant of the first embodiment of the method         according to the invention, a measurement by the technical means         of measurement of a duration T of that sequence of events. The         means 2 then directly measure the duration T of the acoustic or         mechanical signal of the sequence and/or     -   a measurement by the technical means of a mechanical energy S         (in a second variant of the first embodiment of the method         according to the invention) or acoustic energy S_(ac) (in a         seventh variant of the first embodiment of the method according         to the invention) of this event sequence. In this second         variant, the means 2 allow to determine the mechanical energy S         of the sequence from the mechanical signal (obtained from         mechanical sensors such as strain gauges or force gauges being         part of the means 2) associated with the sequence in the         following way: The mechanical energy A_(i) (i=1 to N) of a         damage event of the sequence is determined from the mechanical         signal associated with that event and the means 3 calculate S as         the sum of A_(i) (i=1 to N) where N is the number of damage         events constituting the sequence. In the seventh variant, the         means 2, 22 allow to determine the acoustic energy S_(ac) of the         sequence from the acoustic signal associated with the sequence         in the following way: the means 2, 22 measure the acoustic         energy A_(ac,i) (i=1 to N_(ac)) of an acoustic event of the         sequence from the acoustic signal associated with this event and         the means 3 calculate S_(ac) as the sum of A_(ac,i) (i=1 to         N_(ac)) where N_(ac) is the number of acoustic events         constituting the sequence. The measurement of the mechanical A         and acoustic A_(ac) energy of an event can be obtained with the         help of several sensors spatially distributed around and/or         inside the structure 5, making it possible to locate the event         in the structure and thus to take into account the possible         attenuation of the signal during its propagation in order to         determine with more precision the mechanical A and acoustic         A_(ac) energy of each event and/or     -   in a third variant of the first embodiment of the method         according to the invention, a measurement by the technical means         of measurement 2 of a spatial extension ξ of that sequence of         damage events. In this variant, the means 2 may comprise video         and/or ultrasound and/or image correlation and/or ultrasound         and/or X-ray or other imaging means 6 to visualize the structure         and its damage field in two dimensions or three dimensions and         measure ξ, as explained with reference to FIG. 7 , and/or     -   a measurement, by the technical means of measurement (22 and/or         6), of the number of mechanical events N (in a fourth variant of         the first embodiment of the method according to the invention)         or acoustic events N_(ac) (in a ninth variant of the first         embodiment of the method according to the invention) in that         sequence, and/or         the measurement of an event comprises:     -   a measurement, by the technical means of measurement, of a         mechanical energy A (in a fifth variant of the first embodiment         of the method according to the invention) or acoustic energy         A_(ac) (in an eighth variant of the first embodiment of the         method according to the invention) of this event, and/or     -   a measurement, by the technical means, of a temporal frequency         of mechanical events dN/dt (in a sixth variant of the first         method according to the invention) or acoustic events dN_(ac)/dt         (in a tenth variant of the first method according to the         invention) and/or a rate of dissipated mechanical energy dE/dt         (in an eleventh variant of the method according to the         invention) or a rate of acoustic energy dE_(ac)/dt (in an         eleventh variant of the method according to the invention) at         the time of this event (in a twelfth variant of the method         according to the invention).

Thus, for example, FIG. 2 shows:

-   -   in part (a) the mechanical response of the structure 5 and the         acoustic signal recorded by the sensors 22 during the loading,         and     -   in part (b) the mechanical response of the structure 5 and the         mechanical signal recorded during the loading by the force         gauges and/or strain gauges forming part of the means 2.

The x-axis in FIG. 2 (a) or (b) corresponds to the displacement Δ_(ext) of the wall 7 pressing on the structure in order to exert the force F_(ext) (which is a uni-axial compressive loading) on the structure 5. This x-axis is therefore directly proportional to time t since Δ_(ext)=v_(ext)·t where v_(ext) is the constant displacement speed of wall 7.

The mark 8 in FIG. 2 corresponds to the rupture of the structure 5 and thus to the time t_(c) on the x-axis of FIG. 2 .

In FIG. 2 , we distinguish:

-   -   with reference to the left y-axis, the force F_(ext) (graph 9)     -   with reference to the right y-axis, in part (a) the acoustic         energy S_(ac) of each sequence and in part (b) the mechanical         energy S of each sequence. Each peak 10 in part (b) corresponds         to a sequence (not all of them have a reference, as there are         too many).

We note, with reference to FIGS. 2 and 4 , that:

-   -   there is a ratio greater than or equal to two between the         smallest and largest values of T, S, S_(ac), ξ, N, N_(ac), A,         A_(ac), dN/dt, dN_(ac)/dt, dE/dt or dE_(ac)/dt recorded, and     -   each sequence of events includes at least three events.

FIG. 3 shows the method used to measure the energy S of the mechanical event sequences from the mechanical response in FIG. 2 . Preferably, this is done to measure S. The mechanical energy S dissipated during each sequence is measured from the mechanical response of the structure 5. During each sequence, the response of the structure deviates from the linear elastic behavior. We estimate (see panel FIG. 3(a)) that the applied force remains constant during a sequence, which reproduces the mechanical response that the structure would have had under imposed force loading (our experiments being performed at imposed displacement). An energy balance can then be carried out during a sequence (see panel FIG. 3(b)): the work of the external force ΔW during a sequence counterbalances two otherwise equal contributions: the increase ΔE_(ei) of the elastic energy stored in the structure and the mechanical energy S dissipated by damage during the sequence. S is then obtained by the formula ΔW/2 where ΔW, the work of the external force during the sequence, is equal to the air under the force-displacement graph between the beginning and end of the sequence.

FIG. 4 shows a close-up of a sequence from FIG. 2(a) between Δ_(ext)=13.78 mm and Δ_(ext)=13.92 mm. This sequence is initiated at the time of the force drop F_(ext) and ends when the force drop returns to its initial level. It is composed of a succession of acoustic events whose energy is represented by the vertical bars. Its size S_(ac) is defined as the sum of the energies A_(ac) of each event of that sequence and the number N_(ac) of acoustic events is obtained from the simple count of acoustic events recorded in that sequence.

The x-axis in FIG. 4 corresponds to the displacement Δ_(ext) of the wall 7 pressing on the structure 5 in order to exert the force F_(ext) (which is a uni-axial compressive loading) on the structure 5. This x-axis is therefore directly proportional to time t since Δ_(ext)=v_(ext)·t where v_(ext) is the constant displacement speed of wall 7.

In FIG. 4 , we distinguish:

-   -   with reference to the left y-axis, the force F_(ext) (graph 9)     -   with reference to the right y-axis, the acoustic energy A_(ac)         of each event composing that sequence. Each peak 11 thus         corresponds to an event (not all of them have a reference, as         there are too many). The means 3 thus determine (thanks to the         means 2, in particular the sensors 22):         -   the acoustic energy A_(ac) of each event in the sequence         -   The acoustic energy S_(ac) of the sequence (equal to the sum             of the A_(ac))         -   the number N_(ac) of acoustic events of the sequence         -   the duration T of the sequence

We note that the number of acoustic events N_(ac) in a sequence is not equal to the number N of mechanical events included in that same sequence. These two quantities are related by the scaling law N_(ac)˜N^(α).

The scaling law A_(ac)˜A^(α) relates the average energy of the acoustic events A_(ac) of a sequence with the average energy of the mechanical damage events A during that same sequence. Finally, the relation S_(ac)˜S^(α) makes it possible to link the acoustic energy of a sequence to its mechanical energy.

FIG. 8 shows the evolution of the energy S, the spatial extension ξ of the energy S_(ac), A_(ac), and N_(ac) of the sequences measured on structure 5 during the experiment. The break occurs around 540 s, when ξ reaches the size L of the structure.

Thus, the means 3 determine and/or track the evolution of the energy S (FIG. 8 a ) and/or the spatial extension ξ (FIG. 8 b ), the energy S_(ac) (FIG. 8 c ), the energy A_(ac) (FIG. 8 d ), N_(ac) (FIG. 8 e ) of the energy A, N, of dN/dt, of dN_(ac)/dt, and/or of T of the events or sequences as a function of time t and/or as a function of Δ_(ext) for different events or sequences at different times t of the measurement of an event or sequence of events.

Note in FIG. 4 that each sequence of events may comprise several tens of events.

It is visible in FIG. 4 that the number N_(ac) of acoustic events of the sequence thus determined by the means 3, corresponding to the number of peaks in that FIG. 4 .

FIG. 5 shows a zoom on an event 11 marked by marker 12 in FIG. 4 . This event 11 is characterized by an energy of S_(ac)=220 aJ (aJ meaning attojoule or 10⁻¹⁸ J), a characteristic frequency of 21 kHz and a duration τ_(ac0)=670 μs.

The x-axis in FIG. 5 corresponds to time t.

On FIG. 5 , the acoustic energy (measured in mV by the sensors 22) of this event 11 can be seen with reference to the y-axis. The acoustic energy A_(ac) of this event is calculated as equal or proportional to the square of the envelope of the signal of that event captured by the means 2 and shown in FIG. 5 .

FIG. 6 shows a tracking of the shape of each of the cells composing the structure 5 during the loading 4 Δ_(ext) using the camera 6, so that their displacement as well as their level of damage thus can be tracked, especially for Δ_(ext)=10 mm, Δ_(ext)=15 mm, Δ_(ext)=20 mm, Δ_(ext)=25 mm, and Δ_(ext)=28 mm.

FIG. 7 shows the variation of the damage level of the cells composing the structure 5 between the beginning and the end of a sequence, obtained by the means 3 from the data of FIG. 6 ; this variation makes it possible to obtain an activity map of the sequence (top panels) highlighting (in gray level) the most active zones during the sequence in the structure 5. This activity map corresponds to the mechanical energy density field ρ_(dis) dissipated during the sequence. This map is then thresholded in order to obtain clusters (where adjacent areas wherein the activity exceeds a certain threshold) on the bottom panels, making it possible to define, by means 3, the spatial extension ξ of the sequence. Here, the spatial extension of the sequence is defined as the length, in the direction of the localization band (i.e., the horizontal direction) of the clusters highlighted by the thresholding. This procedure can be used for several sequence(s) as shown for three sequences of different sizes having taken place at different times corresponding respectively to Δ_(ext)=18 mm, Δ_(ext)=22 mm and Δ_(ext)=24 mm. Here we see the increase in spatial extension ξ of the sequences as the structure is closer to failure (which occurs here when Δ_(ext)=26 mm).

Thus, with reference to part b) of FIG. 8 , the means 3 track or determine the progress of the spatial extension ξ of the sequences as a function of time t and/or as a function of Δ_(ext), after a reiteration (preferably at least 10 iterations) over time for different sequences at different instants t of the measurement of a sequence of events (comprising a measurement by the technical means of measurement 2 of a spatial extension ξ of that sequence of events).

By representing the typical size S as a function of the residual lifetime (t_(c)−t) of the structure, the following law was revealed:

S˜(t _(c) −t)^(−β)  (1)

where β=½ (exactly or within 10%). Note that (t_(c)−t) tends to zero as the localization approaches, so equation (1) does reflect the fact that S gets larger and larger as we approach the structure's break.

In the context of the invention, it has been possible to observe that a sequence of size S has the following spatial structure: the locations of damage zones during the sequence are organized into clusters. The size of the largest cluster extends into a disk of characteristic radius

ξ˜S ^(1/df)  (2)

where d_(f)=1.1 (exactly or within 10%) for a two-dimensional structure d_(f)=1.5 (exactly or within 10%) for a three-dimensional structure.

In other words, as a material approaches failure, the sequences of events that characterize its evolution are increasingly large, both in amplitude (energy dissipated) and in size (spatial extension in the material).

According to the invention, theoretical models have been developed to understand these properties. These theoretical developments are based on damage mechanics, extended to the case of heterogeneous materials. From these models, the invention explains the formulas set forth in this description and the value of the exponents involved in these formulas. In particular, these formulas could be extended to the case of three-dimensional materials, with the only difference that the exponent d_(f) which characterizes the relationship between the energy of the event and its spatial extension is equal to d_(f)=1.5 in 3D while it is equal to d_(f)=1.1 in 2D. These theoretical developments support the observations made during the experiments, and in particular the phenomenon of amplification of the damage events as the localization approaches.

A key observation is that the breakup occurs when the spatial extension ξ of the sequences becomes equal to the sample size L. Thus, localization occurs when ξ=L where L is the size of the sample or structure.

Using equation (2), we deduce that the critical size S_(c) (in terms of dissipated energy) of the sequences at break is given by

S _(c) ˜L ^(df)  (3)

The law (3) then makes it possible to foresee and anticipate the rupture. Indeed, S is compared to S_(c). As long as S<<S_(c), structure 5 is far from breaking. The structure or part can safely be used. On the other hand, if S approaches S_(c), it indicates that the break or the failure of the part is imminent. The value of S, which can be measured from a statistical processing of the signals emitted by the structure 5, represents a measure of the good health of the structure. Indeed, the smaller S is compared to the critical value S_(c), the healthier the structure is. On the contrary, the closer S is to the critical value S_(c), the more the structure is in poor health and requires replacement or repair. Appropriate decisions can then be made to minimize the risk of failure by either (i) replacing the part that is about to fail, (ii) repairing the damaged part, or (iii) scrapping the entire structure.

The calculation by means 3 preferably comprises computing the data r=ξ/L representative of the health status of the structure.

-   -   r is between 0 and 1.

The failure corresponds to r=1, for both definitions of L for a structure in compression or tension.

The lower r is than 1, the farther the structure 5 is from failure.

The data r is computed:

-   -   in the third variant, as equal to or proportional to the ratio         ξ/L with L a characteristic size of the structure or material         composing the structure and ξ the measure of a spatial extension         ξ of a sequence of events, and/or     -   in the second or seventh variant, as equal to or proportional to         the ratio ξ/L where L is a characteristic size of the structure         or material composing the structure, ξ depending on the         measurement of the energy respectively S or S_(ac) of a sequence         of events, ξ depending on:         a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or         respectively S or S_(ac) by a relation relating ξ to S^(1/df) or         S_(ac) ^(1/α·df)) respectively,         d_(f) being a constant, α being a constant         ξ depending on S or S_(ac) respectively preferably by the         relation:         respectively d₀·(S/A₀)^(1/df)=ξ or

d ₀·(S _(ac) /A _(ac0))^(1/(α·df))=ξ

Therefore, r is preferably equal or proportional to d₀·(S/A₀)^(1/df)/L or d₀·(S_(ac)/A_(ac0))^(1/(α·df))/L

From S (FIG. 8 a ), the means 3 therefore compute ξ_(S)=d₀·(S/A₀)^(1/df) (shown in FIG. 9 a ) and then r=ξ_(S)/L and/or directly r=ξ_(S)/L=d₀·(S/A₀)^(1/df)/L; and/or

-   -   in the first variant, as equal to or proportional to the ratio         ξ/L where L is a characteristic size of the structure or of the         material composing the structure, ξ depending on the measurement         of the duration T of a sequence of events, ξ depending on:         a constant τ₀ and a constant d₀, and/or         T by a relation relating ξ to (T)^(1/z), z being a constant,         ξ preferably depending on T by the relation ξ=(T/τ₀)^(1/z)·d₀,         where τ₀, d₀ and z are constants.

Therefore, r is preferably equal or proportional to d₀ (T/τ₀)^(1/z)/L

From T, the means 3 therefore compute ξ_(T)=d₀ (T/τ₀)^(1/z) then r=ξ_(T)/L and/or directly r=ξ_(T)/L=d₀ (T/τ₀)^(1/z)/L and/or

-   -   in the fifth or eighth variant, the data r is computed as equal         or proportional to the ratio ξ/L where L is a characteristic         size of the structure or the material of the structure, ξ         depending on the measurement of the respectively mechanical A or         acoustic A_(ac) energy of that event, ξ depending on:         a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or         respectively A or A_(ac) by a relation relating ξ to A^(2/df) or         A_(ac) ^(2/(α·df)) respectively, d_(f) being a constant, α being         a constant         ξ depending on A or A_(ac) respectively preferably by the         relation:         respectively d₀·(A/A₀)^(2/df)=ξ or

d ₀·(A _(ac) /A _(ac0))^(2/(α·df))=ξ

Therefore, r is preferably equal or proportional to d₀·(A/A₀)^(2/df)/L or d₀·(A_(ac)/A_(ac0))^(2/(α·df))/L; and/or

-   -   in the fourth or ninth variant, as equal to or proportional to         the ratio ξ/L where L is a characteristic size of the structure         or material of the structure, ξ depending on the measurement of         the number of respectively mechanical N or acoustic N_(ac)         events in that sequence, ξ depending on:         a constant d₀, and/or         respectively N or N_(ac) by a relation relating ξ to N^(2/df) or         N_(ac) ^(2/(α·df)) respectively,         d_(f) being a constant, α being a constant         ξ depending on N or N_(ac) respectively preferably by the         relation:         respectively d₀·(N)^(2/df)=ξ or

d ₀·(N _(ac))^(2/(α·df))=ξ

Therefore, r is preferably equal or proportional to d₀·(N)^(2/df)/L or d₀·(N_(ac))^(2/(α·df))/L

-   -   in the sixth or tenth variant, as equal or proportional to the         ratio ξ/L with L a characteristic size of the structure or         material composing the structure, ξ depending on the measurement         of the frequency of respectively mechanical dN/dt or acoustic         dN_(ac)/dt events, ξ depending on:     -   a constant ΔT₀ and a constant d₀, and/or     -   respectively dN/dt or dN_(ac)/dt by a relation relating ξ to         (dN/dt)^(2/df) or (dN_(ac)/dt)^(2/(α·df)) respectively, d_(f)         being a constant, α being a constant         ξ depending on dN/dt or dN_(ac)/dt respectively preferably by         the relation:         respectively d₀·(ΔT₀·dN/dt)^(2/df)=ξ or

d ₀·(ΔT ₀ ·dN _(ac) /dt)^(2/(α·df))=ξ

Therefore, r is preferably equal or proportional to d₀·(ΔT₀·dN/dt)^(2/df)/L or d₀·(ΔT₀·dN_(ac)/dt)^(2/(α·df))/L

-   -   ΔT₀ is the average waiting time between two successive         sequences.     -   ΔT₀ is measured by means 2 and/or computed by means 3.         -   in the eleventh or twelfth variant, as equal or proportional             to the ratio ξ/L with L a characteristic size of the             structure or material composing the structure, ξ depending             on the measurement of a dissipated mechanical energy rate             dE/dt or an acoustic energy rate dE_(ac)/dt, ξ depending on:         -   a constant respectively ΔT_(a0) or Δτ_(ac0), and a constant             d₀, and/or         -   respectively dE/dt or dE_(ac)/dt by a relation relating ξ to             (dE/dt)^(1/df) or (dE_(ac)/dt)^(1/(α·df)), d_(f)             respectively, α being a constant     -   ξ depending on dE/dt or dE_(ac)/dt respectively preferably by         the relation:     -   respectively d₀·(ΔT_(a0)·dE/dt)^(1/df)=ξ or

d ₀·(Δτ_(ac0) ·dE _(ac) /dt)^(1/(α·df))=ξ

Therefore, r is preferably equal or proportional to d₀·(ΔT_(a0)·dE/dt)^(1/df)/L or

d ₀·(Δτ_(ac0) ·dE _(ac) /dt)^(1/(α·df)) /L

-   -   ΔT_(a0) (respectively Δτ_(ac0)) are constants equal to the         inverse of the smallest dissipated mechanical energy rate         (respectively acoustic energy rate) generally measured far from         the break.

The value of d₀ is dependent on the material of the structure 5, and is stored by the means 3. d₀ corresponds to the spatial extension of the smallest damage events which can be determined by the means 3 and/or directly in the memory of the means 3. d₀ corresponds to the elementary microstructural size of the material, such as its grain size. In the example of FIG. 1 , d₀ is the diameter of the cylinders composing the cellular material.

-   -   α is equal to 2.6 (exactly or within 10%).

The value of α is stored by the means 3.

The value of d_(f) is stored by the means 3.

-   -   d_(f) is equal to 1.1 (exactly or within 10%) for a         two-dimensional structure and equal to 1.5 (exactly or within         10%) for a three-dimensional structure.

The value of z is stored by the means 3.

-   -   z is equal to 0.57 (exactly or within 10%) for a two-dimensional         structure and equal to 0.65 (exactly or within 10%) for a         three-dimensional structure.

The value of L is dependent on the structure 5, and is stored by the means 3, preferably under two values L=L₁ for the structure 5 in compression and L=L₂ for the structure 5 in tension.

-   -   A₀ (energy of the smallest events) is measured by the device 1         by means 2 (22 and/or 6) and/or calculated by means 3 as for S         and/or stored by means 3.     -   τ₀ (characteristic duration of a damage event) is measured by         the device 1 by the means 2 (22 and/or 6) and/or calculated by         the means 3 (for example, by the data in FIG. 5 ) and/or stored         by the means 3.

Typically, the first embodiment of the method according to the invention comprises:

-   -   a measurement of τ₀ as the smallest measured event duration of         the at least one sequence, and/or     -   a measurement of A₀ or A_(ac0) respectively as the energy of the         smallest mechanical or acoustic events measured from the at         least one sequence.

The first embodiment of the method according to the invention comprises calculating the time t_(c).

In this embodiment, each measurement of a sequence of events or each measurement of an event is measured at a measurement time t.

This first embodiment includes, in particular for the calculation of t_(c):

-   -   a reiteration (preferably at least 10 iterations) in time for         different sequences at different times t of the measurement of a         sequence of events, and/or     -   a reiteration (preferably at least 10 iterations) in time for         different events at different times t of the measurement of an         event

The calculation of the time t_(c) comprising a use and/or an interpolation and/or a regression of a function (the expression interpolation and/or a regression of a function in this description can mean generally a description by a function) relating t_(c), t and one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt, dE/dt, and dE_(ac)/dt, or the temporal evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt, dN_(ac)/dt, dE/dt and dE_(ac)/dt.

-   -   said function preferably comprising:     -   S=B₀/(t_(c)−t)^(β) where B₀ is a constant, in the second         variant, or     -   A=C₀/(t_(c)−t)^(β/2) where C₀ is a constant, in the fifth         variant, or     -   T=D₀/(t_(c)−t)^(β·z/df) where D₀ is a constant, in the first         variant, or     -   ξ=E₀/(t_(c)−t)^(β/df) where E₀ is a constant, in the third         variant, or     -   N=F₀/(t_(c)−t)^(β/2) where F₀ is a constant, in the fourth         variant, or     -   dN/dt=G₀/(t_(c)−t)^(β/2) where G₀ is a constant, in the sixth         variant, or     -   S_(ac)=H₀/(t_(c)−t)^(α·β) where H₀ is a constant, in the seventh         variant, or     -   A_(ac)=K₀/(t_(c)−t)^(α·β/2) where K₀ is a constant, in the         eighth variant, or     -   N_(ac)=L₀/(t_(c)−t)^(α·β/2) where L₀ is a constant, in the ninth         variant, or     -   dN_(ac)/dt=M₀/(t_(c)−t)^(α·β/2) where M₀ is a constant, in the         tenth variant, or     -   dE/dt=N₀/(t_(c)−t)^(β) where N₀ is a constant, in the eleventh         variant, or     -   dE_(ac)/dt=O₀/(t_(c)−t)^(α·β) where O₀ is a constant, in the         twelfth variant,     -   where B₀ C₀ D₀ E₀ F₀ G₀ H₀ K₀ L₀ M₀ N₀ or O₀, respectively, is a         constant whose value is not required for interpolation and/or         regression or the method according to the invention.

The values of β and α are stored by the means 3.

-   -   t_(cur) is the time at which the means 3 determine t_(c), this         calculation being based on several measurements at different         times t before or equal to t_(cur).

Thus, for example, FIG. 10 shows:

-   -   In its part a), the prediction of the time to break t_(c) from         the progress of the energy S of the sequences over the time         range t<t_(cur).     -   In its part b), the predicted breakup time t_(c) ^(predicted) is         plotted as a function of t_(cur) and compared with the breakup         time t_(c) actually measured during the experiment.

Thus, with reference to FIG. 10 , the procedure for predicting the time to break is based on the progress law of the sequence energy, i.e. for instance in the first variant:

S=B ₀/(t _(c) −t)^(β)

-   -   where B₀ is a constant and β=½. From this relation, we can write

S ^(1/β) t=S ^(1/β) t _(c) +B ₀

By introducing the variables Y=S^(1/β)·t and X=S^(1/β), we then obtain the relation:

Y(X)=t _(c) X+B ₀

A linear regression of the function Y(X) then provides the time to break t_(c), which corresponds to the slope of the function Y(X). The uncertainty on t_(c) (shown in FIG. 10 ) is deduced from the quality of the linear regression.

Similarly, all quantities with a power-law relationship with the distance (t_(c)−t) to the break are likely to be used for the prediction of t_(c) on the same principle, according to variants 1 to 10. In particular, the sequence duration T (first variant) as well as their spatial extension ξ (third variant) or N (fourth variant) can be used via the previously described relations.

Alternatively, one can also use the elementary damage events (the energy A of the elementary damage events for the fifth variant or their frequency (number of events per unit time) dN/dt for the sixth variant) to predict the time to failure, as shown in FIG. 11 .

FIG. 11 shows the evolution of the mechanical energy S and acoustic energy S_(ac) of the sequences (panels (a) and (b)), the energy A and A_(ac) of the damage events and acoustic events, their temporal frequency dN/dt and dN_(ac)/dt, and the spatial extension ξ of the sequences, as a function of the residual lifetime (t_(c)−t) of the structure. Power laws are used to predict the time to break to following the procedure with reference to FIG. 10 .

FIG. 13 is an experimental proof of concept of the suitability of the method according to the invention for more complex materials (such as gypsum) than the 2D cellular material of FIG. 1 or 6 .

The sample is a plaster cylinder (diameter—20 mm; height—30 mm).

This FIG. 13 (taken from experiments performed on plaster samples, i.e. on a three-dimensional material, which is widely used in civil engineering) shows:

-   -   in its part a), the experimental device including in particular         the device allowing the measurement of the acoustic events (but         not measurements by camera, which are useless here because the         plaster is three-dimensional). This FIG. 13 a ) is analogous to         FIG. 1(a) and the common reference numbers are therefore not         described again.     -   in its part b), the mechanical force-displacement response of         the sample (indicating the break at the force peak) as well as         the evolution in time (and acceleration near the break) of the         acoustic events. This FIG. 13 b ) is analogous to FIG. 2(a) and         the common reference numbers are therefore not described again.     -   in its part c), the prediction of the residual lifetime from the         method according to the invention. This FIG. 13 c ) is analogous         to FIG. 10(a) or (b) and the common reference numbers are         therefore not described again. Here, we show that acoustic         events can also be used to predict failure (the previous example         on 2D cellular material used mechanical events)

The table below summarizes the method for computing r:

TABLE 2 Data measured by Formula used by Variant Parameter Prediction the means 2 the means 3 (1) ξ $r_{\xi} = \frac{\xi}{L}$ ξ, L — (2) ξ_(s) $r_{\xi_{s}} = \frac{\xi_{s}}{L}$ S, L $\begin{matrix} {\frac{\xi_{s}}{d_{o}} = \left( \frac{S}{A_{o}} \right)^{\frac{1}{d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)}} \end{matrix}$ (3) ξ_(T) $r_{\xi_{T}} = \frac{\xi_{T}}{L}$ T, L $\begin{matrix} {\frac{\xi_{T}}{d_{o}} = \left( \frac{T}{\tau_{o}} \right)^{\frac{1}{z}}} \\ {{z = {0.57\left( {2d} \right)}};{0.65\left( {3d} \right)}} \end{matrix}$ (4) ξ_(A) $r_{\xi_{\langle A\rangle}} = \frac{\xi_{\langle A\rangle}}{L}$ A, L $\begin{matrix} {\frac{\xi_{A}}{d_{o}} = \left( \frac{A}{A_{o}} \right)^{\frac{2}{d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)}} \end{matrix}$ (5) ξ_(N) $r_{N_{A}} = \frac{\xi_{N}}{L}$ N, L $\begin{matrix} {\frac{\xi_{N_{A}}}{d_{o}} = (N)^{\frac{2}{d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)}} \end{matrix}$ (6) $\xi_{\frac{dN}{dt}}$ $r_{N_{A}} = \frac{\xi_{\frac{dN}{dt}}}{L}$ $\frac{dN}{dt},L$ $\begin{matrix} {\frac{\xi_{N_{A}}}{d_{o} =} = \left( {\Delta T_{o}\frac{dN}{dt}} \right)^{\frac{2}{d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)}} \end{matrix}$ (7) ξ_(s) _(ac) $r_{s_{ac}} = \frac{\xi_{s}}{L}$ S_(ac), L $\begin{matrix} {\frac{\xi_{s_{ac}}}{d_{o}} = \left( \frac{S_{ac}}{A_{ac_{o}}} \right)^{\frac{1}{\alpha d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)};{\alpha = 2.6}} \end{matrix}$ (8) ξ_(s) _(ac) $r_{A_{ac}} = \frac{\xi_{A_{ac}}}{L}$ A_(ac), L $\begin{matrix} {\frac{\xi_{A_{ac}}}{d_{o}} = \left( \frac{A_{ac}}{A_{ac_{o}}} \right)^{\frac{2}{({ad_{f}})}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)}} \end{matrix}$ (9) ξ_(N) _(ac) $r_{N_{ac}} = \frac{\xi_{N_{ac}}}{L}$ N_(ac), L $\begin{matrix} {\frac{\xi_{N_{ac}}}{d_{o}} = \left( N_{ac} \right)^{\frac{2}{({ad_{f}})}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)};{\alpha = 2.6}} \end{matrix}$ (10)  $\xi_{\frac{{dN}_{ac}}{dt}}$ $r_{N_{ac}} = \frac{\xi_{\frac{{dN}_{ac}}{dt}}}{L}$ $\frac{{dN}_{ac}}{dt},L$ $\begin{matrix} {\frac{\xi_{N_{ac}}}{d_{o}} = \left( {\Delta T_{o}\frac{{dN}_{ac}}{dt}} \right)^{\frac{2}{\alpha d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)};{\alpha = 2.6}} \end{matrix}$ (11)  $\xi_{\frac{dE}{dt}}$ $r_{\xi_{A}} = \frac{\xi_{\frac{dE}{dt}}}{L}$ $\frac{dE}{dt},L$ $\begin{matrix} {\frac{\xi_{\frac{dE}{dt}}}{d_{o}} = \left( {\Delta T_{ao}\frac{dE}{dt}} \right)^{\frac{1}{d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)}} \end{matrix}$ (12)  $\xi_{\frac{{dE}_{ac}}{dt}}$ $r_{A_{ac}} = \frac{\xi_{\frac{{dE}_{ac}}{dt}}}{L}$ $\frac{{dE}_{ac}}{dt},L$ $\begin{matrix} {\frac{\xi_{\frac{{dE}_{ac}}{dt}}}{d_{o}} = \left( {\Delta T_{aco}\frac{{dE}_{ac}}{dt}} \right)^{\frac{1}{\alpha d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)};{\alpha = 2.6}} \end{matrix}$

The table below summarizes the method for computing t_(c):

TABLE 3 Data measured Formula used by the Variant Parameters by the means 2 means 3 (1) T T, t $\begin{matrix} {T \sim \left( {t_{c} - t} \right)^{{- \beta} \cdot \frac{z}{d_{f}}}} \\ {{{\beta \cdot \frac{z}{d_{f}}} = {0.26\left( {2d} \right)}};{0.22\left( {3d} \right)}} \end{matrix}$ (2) S S, t $\begin{matrix} {S \sim \left( {t_{c} - t} \right)^{- \beta}} \\ {\beta = \frac{1}{2}} \end{matrix}$ (3) ξ ξ, t $\begin{matrix} {\xi \sim \left( {t_{c} - t} \right)^{- \frac{\beta}{d_{f}}}} \\ {{d_{f} = {1.1\left( {2d} \right)}};{1.5\left( {3d} \right)}} \end{matrix}$ (4) N N, t $\begin{matrix} {N \sim \left( {t_{c} - t} \right)^{- \frac{\beta}{2}}} \\ {\beta = \frac{1}{2}} \end{matrix}$ (5) A A, t $\begin{matrix} {A \sim \left( {t_{c} - t} \right)^{- \frac{\beta}{2}}} \\ {\beta = \frac{1}{2}} \end{matrix}$ (6) $\frac{dN}{dt}$ $\frac{dN}{dt},t$ $\begin{matrix} {\frac{dN}{dt} \sim \left( {t_{c} - t} \right)^{- \frac{\beta}{2}}} \\ {\beta = \frac{1}{2}} \end{matrix}$ (7) S_(ac) S_(ac), t $\begin{matrix} {S_{ac} \sim \left( {t_{c} - t} \right)^{{- \alpha}\beta}} \\ {{\beta = \frac{1}{2}};{\alpha = 2.6}} \end{matrix}$ (8) A_(ac) A_(ac), t $\begin{matrix} {A_{ac} \sim \left( {t_{c} - t} \right)^{- \frac{\alpha\beta}{2}}} \\ {{\beta = \frac{1}{2}};{\alpha = 2.6}} \end{matrix}$ (9) N_(ac) N_(ac), t $\begin{matrix} {N_{ac} \sim \left( {t_{c} - t} \right)^{- \frac{\alpha\beta}{2}}} \\ {{\beta = \frac{1}{2}};{\alpha = 2.6}} \end{matrix}$ (10)  $\frac{dN_{ac}}{dt}$ $\frac{dN_{ac}}{dt},t$ $\begin{matrix} {\frac{dN_{ac}}{dt} \sim \left( {t_{c} - t} \right)^{- \frac{\alpha\beta}{2}}} \\ {{\beta = \frac{1}{2}};{\alpha = 2.6}} \end{matrix}$ (11)  $\frac{dE}{dt}$ $\frac{dE}{dt},t$ $\begin{matrix} {\frac{dE}{dt} \sim \left( {t_{c} - t} \right)^{- \beta}} \\ {\beta = \frac{1}{2}} \end{matrix}$ (12)  $\frac{dE_{ac}}{dt}$ $\frac{dE_{ac}}{dt},t$ $\begin{matrix} {\frac{dE_{ac}}{dt} \sim \left( {t_{c} - t} \right)^{{- \alpha}\beta}} \\ {{\beta = \frac{1}{2}};{\alpha = 2.6}} \end{matrix}$

The table below summarizes the values of the exponents z and d_(f):

TABLE 4 Case z d_(f) βz/d_(f) Two-dimensional structure 5 0.57 1.10 0.26 Three-dimensional structure 5 0.65 1.50 0.22

The prediction of the failure of structures or mechanical parts is a major issue in all industrial sectors for which the mechanical strength of materials plays an important role. We cite here as examples three possible implementations of the invention in three distinct domains:

-   -   (i) nuclear: nuclear structures, both metal alloy tanks and         concrete structures of power plants, are subject to high         stresses (mechanical, but also sometimes thermal or even         radioactive) that put their mechanical integrity to a severe         test, over particularly long periods of time, up to several         decades. These structures or materials are heavily monitored, as         risk prevention in this type of activity is central. Access to         the signals needed to implement the technology is therefore         relatively easy. The method described in this invention         potentially makes it possible to decipher these signals, and         thus to estimate the state of damage of the structure as well as         the duration over which it can still remain in service.     -   (ii) aeronautics: the materials used in the fuselage of an         aircraft (such as its wings) are particularly closely monitored,         because of the serious accidents that a rupture could cause. The         proposed technology makes it possible to translate the signals         (of deformation, acoustic emission, etc.) measured in situ, in         flight or at rest, in terms of damage level. It makes it         possible to thus determine the level of wear of the device. This         analysis can help to establish more precisely the number of         flights that an aircraft can still make before being scrapped, a         matter that remains a major technological and commercial issue         in this sector.     -   (iii) civil engineering. Important structures such as dams or         bridges are monitored with sensors to assist the engineer in         determining the risk of failure. However, determining the         mechanical health of the structure remains a particularly         difficult task. The technology according to the invention makes         it possible to quantitatively analyze the signals recorded on         the structure, and to implement the most precise risk prevention         policy possible, while allowing an estimate of the remaining         life of the structure.

This list is far from being exhaustive and the applications of the invention relates to all industrial fields for which the mechanical strength of a part or structure is an important issue.

Of course, the invention is not limited to the examples just described, and many adjustments can be made to these examples without going beyond the scope of the invention.

Of course, the various features, forms, variants and embodiments of the invention may be combined with each other in various combinations as long as they are not incompatible or exclusive of each other. In particular, all the variants and embodiments described above can be combined with each other. 

1. A method for analyzing a structure, comprising: for at least one sequence of several events located inside the structure, each event being a mechanical damage event or an acoustic event: a measurement of a sequence of said events comprising a measurement by technical means of measurement of a duration T, a mechanical S or acoustic energy S_(ac) and/or a spatial extension ξ of that sequence and/or a number of mechanical N or acoustic N_(ac) events in that sequence and/or of the mechanical A or acoustic A_(ac) energies of the events of that sequence; and/or a measurement of an event comprising a measurement by the technical means of measurement of a mechanical energy A or acoustic energy A_(ac) of this event, and/or of a temporal frequency of mechanical events dN/dt or acoustic events dN_(ac)/dt at the time of this event and/or of a dissipated mechanical energy rate dE/dt or of an acoustic energy rate dE_(ac)/dt at the time of this event; and according to the measurement of an event and/or the measurement of a sequence of events, a calculation by technical means of calculation of a data r representative of a state of health of the structure or of a time t_(c) to failure of the structure.
 2. The method according to claim 1, characterized in that the measurement of a sequence of events comprises a measurement by the technical means of measurement of a duration T of that sequence of events.
 3. The method according to claim 1, characterized in that the measurement of a sequence of events comprises a measurement by the technical means of measurement of a mechanical energy S or acoustic energy S_(ac) of that sequence of events.
 4. The method according to claim 3, characterized in that the measurement of mechanical energy S or acoustic energy S_(ac) is obtained by several sensors spatially distributed around and/or inside the structure.
 5. The method according to claim 1, characterized in that the measurement of a sequence of events comprises a measurement by the technical means of measurement of a spatial extension ξ of that sequence of events.
 6. The method according to claim 1, characterized in that the measurement of an event comprises a measurement by the technical means of measurement of a mechanical energy A or acoustic energy A_(ac) of that event.
 7. The method according to claim 1, characterized in that the measurement of a sequence of events comprises a measurement by the technical means of measurement of the number of mechanical events N or acoustic events N_(ac) in that sequence.
 8. The method according to claim 1, characterized in that the measurement of an event comprises a measurement by the technical means of measurement of a temporal frequency of mechanical events dN/dt or acoustic events dN_(ac)/dt.
 9. The method according to claim 1, characterized in that the calculation comprises a calculating of the data r representative of the health status of the structure.
 10. The method according to claim 5, characterized in that the calculation comprises a calculating of the data r representative of the health status of the structure, and in that the data r is computed as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or material composing the structure and ξ the measure of a spatial extension ξ of a sequence of events.
 11. The method according to claim 3, characterized in that the calculation comprises a calculating of the data r representative of the health status of the structure and in that the data r is computed as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or the material composing the structure, ξ depending on the measurement of the energy respectively S or S_(ac) of a sequence of events, ξ depending on: a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or respectively S or S_(ac) by a relation relating ξ to S^(1/df) or S_(ac) ^(1/(α·df)) respectively, d_(f) being a constant, α being a constant ξ depending on S or S_(ac) respectively preferably by the relation: respectively d₀·(S/A₀)^(1/df)=ξ or d ₀·(S _(ac) /A _(ac0))^(1/(α·df))=ξ.
 12. The method according to claim 11, characterized in that a is substantially equal to 2.6, and/or d_(f) is substantially equal to 1.1 for a two-dimensional structure and substantially equal to 1.5 for a three-dimensional structure.
 13. The method according to claim 2, characterized in that the calculation comprises a calculating of the data r representative of the health status of the structure and in that the data r is computed as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or the material composing the structure, ξ depending on the measurement of the duration T of a sequence of events, ξ depending on: a constant τ₀ and a constant d₀, and/or T by a relation relating ξ to (T)^(1/z), z being a constant, ξ preferably depending on T by the relation ξ=(T/τ₀)^(1/z)·d₀.
 14. The method according to claim 11, characterized in that it comprises: a measurement of τ₀ as the smallest measured event duration of the at least one sequence, and/or a measurement of A₀ or A_(ac0) respectively as the energy of the smallest mechanical or acoustic events measured from the at least one sequence.
 15. The method according to claim 6, characterized in that the calculation comprises a calculating of the data r representative of the health status of the structure and in that the data r is computed as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or the material of the structure, ξ depending on the measurement of the energy respectively A or A_(ac) of a sequence of events, ξ depending on: a constant, respectively A₀ or A_(ac0) and a constant d₀, and/or respectively A or A_(ac) by a relation relating ξ to A^(2/df) or A_(ac) ^(2/(α·df)) respectively, d_(f) being a constant, α being a constant ξ depending on A or A_(ac) respectively preferably by the relation: respectively d₀·(A/A₀)^(2/df)=ξ or d ₀·(A _(ac) /A _(ac0))^(2/(α·df))=ξ.
 16. The method according to claim 7, characterized in that the calculation comprises a calculating of the data r representative of the health status of the structure and in that the data r is computed as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or the material of the structure, ξ depending on the measurement of the respectively mechanical N or acoustic N_(ac) energy in that sequence, ξ depending on: a constant d₀, and/or respectively N or N_(ac) by a relation relating ξ to N^(2/df) or N_(ac) ^(2/(α·df)) respectively, d_(f) being a constant, α being a constant ξ depending on N or N_(ac) respectively preferably by the relation: respectively d₀·(N)^(2/df)=ξ or d ₀·(N _(ac))^(2/(α·df))=ξ.
 17. The method according to claim 8, characterized in that the calculation comprises a calculating of the data r representative of the health status of the structure and in that the data r is computed as equal to or proportional to the ratio ξ/L with L a characteristic size of the structure or the material of the structure, ξ depending on the measurement of the frequency of respectively mechanical dN/dt or acoustic dN_(ac)/dt events, ξ depending on: a constant ΔT₀ and a constant d₀, and/or respectively dN/dt or dN_(ac)/dt by a relation relating ξ to (dN/dt)^(2/df) or (dN_(ac)/dt)^(2/(α·df)) respectively, d_(f) being a constant, α being a constant ξ depending on dN/dt or dN_(ac)/dt respectively preferably by the relation: respectively d₀·(ΔT₀·dN/dt)^(2/df)=ξ or d ₀·(ΔT ₀ ·dN _(ac) /dt)^(2/(α·df))=ξ.
 18. The method according to claim 1, characterized in that the computing comprises computing the time t_(c).
 19. The method according to claim 18, characterized in that the measurement of event sequences or the measurement of events may be measured in such a way as to determine and/or track a time evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt and dN_(ac)/dt, dE/dt and dE_(ac)/dt as a function of the measurement time t, the calculation of the time t_(c) comprising a use and/or an interpolation and/or a regression of a function relating t_(c), t and the temporal evolution of one of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt, dN_(ac)/dt, dE/dt and dE_(ac)/dt said function preferably comprising: S=B₀/(t_(c)−t)^(β) where B₀ is a constant, or A=C₀/(t_(c)−t)^(β/2) where C₀ is a constant, or T=D₀/(t_(c)−t)^(β·z/df) where D₀ is a constant, or ξ=E₀/(t_(c)−t)^(β/df) where E₀ is a constant, or N=F₀/(t_(c)−t)^(β/2) where F₀ is a constant, or dN/dt=G₀/(t_(c)−t)^(β/2) where G₀ is a constant, or S_(ac)=H₀/(t_(c)−t)^(αβ) where H₀ is a constant, or A_(ac)=K₀/(t_(c)−t)^(αβ/2) where K₀ is a constant, or N_(ac)=L₀/(t_(c)−t)^(αβ/2) where L₀ is a constant, or dN_(ac)/dt=M₀/(t_(c)−t)^(αβ/2) where M₀ is a constant, or dE/dt=N₀/(t_(c)−t)^(β) where N₀ is a constant, or dE_(ac)/dt=O₀/(t_(c)−t)^(α·β) where O₀ is a constant, where preferably β=0.5 and α=2.6.
 20. The method according to claim 18, wherein there is a ratio greater than or equal to two between the smallest and largest values of T, S, S_(ac), ξ, N, N_(ac), A, A_(ac), dN/dt, dN_(ac)/dt, dE/dt or dE_(ac)/dt recorded.
 21. The method according to claim 1, characterized in that each sequence of events comprises at least five events.
 22. A device for analyzing a structure, comprising: for at least one sequence of several events located inside the structure, each event being a mechanical damage event or an acoustic event, technical means of measurement: arranged to measure a sequence of said events comprising a measurement by technical means of a duration T, a mechanical S or acoustic energy S_(ac) and/or a spatial extension ξ of that sequence and/or a number of mechanical N or acoustic N_(ac) events in that sequence and/or of the mechanical A or acoustic A_(ac) energies of the events of that sequence; and/or arranged to measure an event comprising a measurement by the technical means of measurement of a mechanical energy A or acoustic energy A_(ac) of this event, and/or of a temporal frequency of mechanical events dN/dt or acoustic events dN_(ac)/dt at the time of this event, and/or of a dissipated mechanical energy rate dE/dt or of an acoustic energy rate dE_(ac)/dt at the time of this event; and computing means arranged and/or programmed to compute, as a function of the measurement of an event and/or the measurement of a sequence of events, a data r representative of a state of health of the structure or of a time t_(c) to failure of the structure. 